Heat the olive oil in a heavy-based frying pan.

Add onions and garlic to the pan, reduce heat to low, and cook for 20 minutes, stirring frequently until the onions are very soft and translucent.

Remove the pan from heat and let the mixture cool completely.

Transfer the cooled onion and garlic mixture to a food processor.

Add the seeded and sliced Thai chiles and dark brown sugar to the food processor.

Blend the ingredients until smooth.

Return the blended mixture to the frying pan.

Cook over medium-low heat for approximately 10 minutes, stirring frequently, until the liquid evaporates and the mixture achieves a jam-like consistency.

Allow the chili jam to cool slightly before serving.

Store the jam in an airtight jar in the refrigerator for up to 1 week.